(1) Field of the Invention
The present invention relates to a control apparatus for a multiprocessor. The present invention particularly relates to a technology for reducing power consumption by the control apparatus.
(2) Related Art
In distributed processing, a multiprocessor occasionally has to perform synchronization to pass data among processors therein, or to maintain consistency among processing orders and among values generated by operations. Here, synchronization indicates that a processor, having finished its own processing, waits till other processors end their processing. When all the processors, among which consistency of operation values should be maintained, end their operations, every processor in wait state can go on to a subsequent operation respectively.
In such a multiprocessor system, power saving is attempted by stopping power supply to a processor brought to a wait state, and resuming the power supply when all the processors have ended their operations (e.g. Japanese Laid-open Patent Application No. H7-146846).
However, such power saving in a multiprocessor system has the following problem. When power supply resumes for a processor having been in wait state, it requires a certain amount of time before the power supply voltage stabilizes. This means that a subsequent operation cannot be started immediately, impairing processing speed for the entire operations.
Furthermore, in stopping power supply, each processor has to save the context stored so far in its register (e.g. operation result or processing status) to a memory and so on, in fear of losing the context. Accordingly, after the synchronization and the resumption of power supply, a processor has to read the saved context for having its register reflect the context, which also takes some time. In addition, since such context restoration is performed after the power supply voltage has stabilized, the processing speed for the entire operations will be further impaired.